WHAT ARE PESTICIDES?
Pesticides are substances or mixtures that are used to prevent, destroy or control pests.
Pests can be insects, diseases (fungi, bacteria), nematodes or weeds.
Pesticides can be classified as chemical pesticides or biopesticides. Biopesticides are made of naturally occurring substances.
Pesticides can also be classified based on:
- Their target destination
- Their chemical structure.
- Their mode of action.
THE TARGET DESTINATIONS OF PESTICIDES
Insecticides – Pesticides that kill or damage insects.
Fungicides – Pesticides that are used against fungi .
Herbicides – pesticides that kill weeds.
Nematicides – pesticides that kill nematodes.
Other types of pesticides include rodenticides and molluscicides.
THE CHEMICAL GROUPS OF PESTICIDES
Pesticides that are composed of chemical compounds, can be further categorized into groups.
- Carbamates (insecticides, herbicides, fungicides)
- Neonicotinoids (pesticides)
- Pyrethroids (insecticides)
- Organophosphorus (insecticides, herbicides, fungicides)
- Phenyl-amides (fungicides).
- Organochlorines (insecticides, herbicides)
Organophosphates are a result of the reaction of phosphoric acid and alcohol.
Common insecticides that belong to the organophosphates group include malathion, parathion, diazinon, fenthion, dichlorvos, chlorpyrifos and ethion.
Organophosphates inhibit cholinesterase and according to the EPA, all organophosphates are toxic to the nervous system.
Organophosphates were were widely used in the past, however today, many of them are banned in developed countries due to their high toxicity to human and animals.
Glyphosate is a common organophosphate herbicide.
Carbamates are organic compounds derived from carbamic acid.
They are used as insecticides, fungicides, herbicides or nematicides.
Common Pesticides – methiocarb, metiram (fungicide), pirimiarb
Like organophosphates, they inhibit the acetylcholinesterase enzyme, but their effect is more reversible and less severe.
Pyrethroids are synthetic analogues of the natural substance pyrethrin, which is obtained from chrysanthemum flowers. They affect the sodium channels in the nervous system of insects.
Pyrethroids are used as contact insecticides and act quickly. They are not very toxic to mammals and are biodegradable.
Neonicotinoids are systemic pesticides that are related to nicotine.
They act on the nervous system of the insect and are efficient against sap sucking pests and some beetles.
The first neoniconoid was registered in Europe in 2005.
In April 2018, the European Union banned the use of Imidacloprid, clothianidin and thiamethoxam in open spaces, due to its toxicity to bees.
CONTACT AND SYSTEMIC PESTICIDES
Contact pesticides – contact pesticides are effective when they come in direct contact with the pathogen and their activity is limited to the place where they were applied.
Systemic pesticides – absorbed by the plant. Depending on the type of pesticide and its properties, they can be applied to the soil or leaves.
Translaminar pesticides – “locally systemic” can move from the upper side of the leaf to the lower part, which was not sprayed.
MODE OF ACTION OF PESTICIDES
Mode of action of a pesticide is the way in which it interferes with the growth and reproduction of the pest or disease.
The chemical structure of the active ingredient of the insecticide generally defines its mode of action.
Classification of modes of action of insecticides:
WHY IS IT IMPORTANT TO UNDERSTAND THE MODE OF ACTION?
Understanding the mode of action helps to determine how to use the pesticide optimally.
It helps to understand the mechanisms of selectivity and resistance as well as the toxicity of the pesticide to beneficial insects, fish, birds and other animals.
In a spray program it is highly recommended to alternate pesticides that have different modes of action and not to use pesticides of the same mode of action in successive applications.
IRAC, FRAC and HRAC classification codes provide information on the mode of action of the pesticide.